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Table 1. Commonly grown vegetables and their plant families.

Alliaceae Brassicaceae Cucurbitacae Fabaceae Solanaceae

ChivesGarlicLeeksOnions

BroccoliBrussel sproutsCabbageCauliflowerCollardsLettuceMustardRadishRutabagaSpinachTurnip

CantaloupeCucumbersHoneydew melonsPumpkinsSquashWatermelon

All beansEnglish peasSouthern peas

EggplantPeppersPotatoesTomatoes

Asteraceae Poaceae Malvaceae Chenopodiaceae Apiaceae

Lettuce Corn Okra Spinach Carrot

Seed of some vegetable varieties, however, arenot produced in the west, and local seed must beused. Purchase seed from a reputable dealerbecause you cannot distinguish healthy seedfrom diseased seed.

Seed are protected by fungicides often appliedto the seed by the company. Seed can also betreated by the home gardener. These treatmentsgive young seedlings some protection from soil-borne pathogens as they germinate and emerge.They do not, however, control pathogens thatmay attack the plant after the seedling stage.Some pathogens are carried on the surface ofseed and can be controlled with fungicide treat-ment. Fungicides are not effective on pathogenscarried beneath the seed coat.

Gardeners starting a crop from transplantsshould examine transplants carefully before pur-chasing. Select healthy transplants that appeardisease and insect free.

Use Resistant VarietiesUsing resistant varieties is the most efficient

way of controlling vegetable diseases. Make aneffort to buy resistant varieties when they areavailable. Seed catalogs generally list resistanttraits of different vegetable varieties.

For example, disease resistant tomatoes aredesignated “VFN.” These letter indicate resis-tance to Verticillium wilt (not common in Georgia),Fusarium wilt and nematodes. In tomatoes, thereis also resistance to Stemphyllium (gray leaf spot)= S, Tobacco Mosaic Virus = TMV, Alternariaalternata stem canker = A or ASC, Septoria leaf

spot = L and Tomato Spotted Wilt = TSW.Other vegetables such as squash, pepper,

beans and peas also have disease and nematoderesistance. Note that plant disease and nematoderesistance are relative terms, as resistant vari-eties have differing levels of resistance. Resist-ance does not always mean the plants are im-mune to these problems. Some seed catalogsmay indicate tolerance to a certain pest.Tolerance usually indicates that a particularvariety of vegetable may produce fruit of accept-able yield and quality while exhibiting moderateto high levels of disease.

Planting Date ManagementPlanting dates can be an effective tool for dis-

ease management. Follow the recommendedplanting dates for the particular vegetable grown.For example, okra should be planted when soiltemperatures are warm for good germination andgrowth. Planting this crop when soil tempera-tures are cool can cause increased incidence ofsoil-borne diseases such as soreshin and damp-ing-off.

Using transplants may help avoid early dis-ease problems so long as the transplants arefrom a reputable source and are disease free.Plant crops such as corn and beans earlier,because their seeds germinate in cooler soils. Itis also advantageous to plant these particularcrops early to escape severe virus infections. Thisis particularly true with squash. Aphids, whichtransmit many virus diseases, are at lower popu-lation levels early in the season. High aphid pop-

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ulations late in the season can lead to more virusproblems.

Trap CropsUsing trap crops may sometimes help manage

virus diseases and aphid populations. A few rowsof a trap crop around the vegetable garden (suchas rye or corn) will cause aphids to feed therefirst, possibly loosening the virus they may carry.Trap crops can limit aphid damage and help re-duce the incidence of virus diseases, which aresometimes severe on beans, cucurbits and solan-aceous crops.

Proper Spacing and TrellisingProper spacing and trellising can reduce the

occurrence of vegetable diseases. Space plantsproperly to allow growth and air circulation.Humid and wet conditions occur if plants arecrowded and unable to dry quickly. Extendedperiods of wet foliage are ideal for development offungal and bacterial diseases. Crowded plantstake longer to dry and provide favorable diseaseconditions. Crop protectants also cannot pene-trate dense foliage, thus limiting their effective-ness.

Staking or trellising tomatoes, pole of halfrunner beans, and cucumbers will prevent soilcontact with the foliage and fruit. Air circulationwill be better if these plants are trellised, promot-ing foliage drying and reducing disease severity.Limiting soil-plant contact reduces diseases suchas fruit rots. Crop protectants also can be moreeffectively applied to trellised plants.

Proper Watering PracticesAvoid excessive soil moisture. Over-watering

enhances seed decay, damping-off, and root andcrown rot diseases. Choanephora fruit rot, whichcauses the whisker-like blossom end rot, can beincreased by over-watering.

If possible, irrigate by running water betweenthe rows. Avoid splashing plants with soil, sinceany potential pathogens are soil-borne. Drip irri-gation is also a good method of watering withoutwetting foliage. Drip irrigation uses either a hoseor tape that allows water to be applied slowlyover time at the base of the plant or just beneaththe soil surface. Garden drip irrigation kits arereadily available.

Avoid wetting the foliage when watering. Wetfoliage is favorable for development of most foliarfungal and bacterial diseases. If wetting the

foliage is unavoidable, irrigate in the morning sofoliage can completely dry before evening.

Maintain uniform soil moisture. This canreduce problems such as blossom end rot (cal-cium deficiency) of tomatoes and peppers.

Don’t work in the garden when plants and soilare wet. Bacterial and fungal diseases spreadeasily from one plant to another by hands andclothing when above-ground plant parts are wet.

Use a Mulch LayerUse a mulch layer of straw, bark, shredded

paper or plastic to prevent soil from splashingonto plants and to prevent fruit from touchingthe bare ground. This will help prevent rots onmature fruit such as strawberries, tomatoes,squash, cucumbers and melons. Mulches alsoare a sound cultural practice to help conservesoil moisture and reduce weed infestations.

Proper FertilizationAdequate and proper fertilization helps pre-

vent vegetable diseases. Test soil three to sixmonths before the growing season, and follow therecommendations to supply appropriate nutrientrequirements and adjust soil pH. Avoid excessiveamounts of nitrate forms of nitrogen, whichencourage root rot diseases. Use ammoniumforms instead (no more than 50 percent). Be surethe soil pH level is in the proper range for a par-ticular crop. Proper pH prevents blossom end rotand encourages healthy growth of tomatoes andpeppers.

Weed Free GardenWeeds in the same families as some of the

vegetable crops can be another source of dis-eases and insects. For example, some weeds canserve as virus reservoirs for several insect-transmitted viruses that can infect homegrownvegetables. Good weed control will increase airmovement in the garden and decrease conditions— such as excessive moisture — that favordisease development.

Avoid Tobacco whenWorking in the Garden

If you use tobacco, wash your hands tho-roughly before handling plants. This practice willprevent the spread of tobacco mosaic virus,which can infect many different kinds of

Reviewed May 2009